There is a recently renewed interest on the study of single and double charge exchange reactions with heavy ions. We report here a preliminary theoretical study of double charge exchange reactions in terms of two successive charge exchanges in 2nd order Distorted Wave Born approximation. This allows us to include the effect of the different transfer channels in an approximate way. Evidences show that the charge exchange process is dominant. The following one in importance is the combination of one single charge exchange, one neutron pick-up and one proton stripping. This particular process calls for further investigation. ; Spanish Ministerio de Economía y Competitividad FIS2014-53448-C2-1-P ; FEDER Funds FIS2014-53448-C2-1-P ; Junta de Andalucía 654002 ; European Union 654002
[EN] Colloidal quantum dot solar cells achieve spectrally selective optical absorption in a thin layer of solution-processed, size-effect tuned, nanoparticles. The best devices built to date have relied heavily on drift-based transport due to the action of an electric field in a depletion region that extends throughout the thickness of the quantum dot layer. Here we study for the first time the behaviour of the best-performing class of colloidal quantum dot films in the absence of an electric field, by screening using an electrolyte. We find that the action of selective contacts on photovoltage sign and amplitude can be retained, implying that the contacts operate by kinetic preferences of charge transfer for either electrons or holes. We develop a theoretical model to explain these experimental findings. The work is the first to present a switch in the photovoltage in colloidal quantum dot solar cells by purposefully formed selective contacts, opening the way to new strategies in the engineering of colloidal quantum dot solar cells. ; We thank the following agencies for support of this research: Ministerio de Educacion y Ciencia under project HOPE CSD2007-00007, Generalitat Valenciana (ISIC/2012/008) and Universitat Jaume I project 12I361.01/1. EHS and KWK acknowledge the Award KUS-11-009-21, made by King Abdullah University of Science and Technology (KAUST) and the International Cooperation of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (2012T100100740). ; Mora-Sero, I.; Bertoluzzi, L.; González-Pedro, V.; Gimenez, S.; Fabregat-Santiago, F.; Kemp, KW.; Sargent, EH. (2013). Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics. Nature Communications. 4:3272-3272. https://doi.org/10.1038/ncomms3272 ; S ; 3272 ; 3272 ; 4 ; Grätzel, M., Janssen, R. A. J., Mitzi, D. B. & Sargent, E. H. Materials interface engineering for solution-processed photovoltaics. Nature ...
[EN] Electron transfer involving nucleic acids and their derivatives is an important field in bioorganic chemistry, specifically in connection with its role in the photo-driven DNA damage and repair. Four-membered ring heterocyclic oxetanes and azetidines have been claimed to be the intermediates involved in the repair of DNA (6-4) photoproduct by photolyase. In this context, we examine here the redox properties of the two azetidine isomers obtained from photocycloaddition between 6-aza-1,3-dimethyluracil and cyclohexene. Steady-state and time-resolved fluorescence experiments using a series of photoreductants and photooxidants have been run to evaluate the efficiency of the electron transfer process. Analysis of the obtained quenching kinetics shows that the azetidine compounds can act as electron donors. Additionally, it appears that the cis isomer is more easily oxidized than its trans counterpart. This result is in agreement with electrochemical studies performed on both azetidine derivatives. ; Spanish Government (CTQ2015-70164-P, RIRAAF RETICS RD12/0013/0009, Red de Fotoquimica Biologica CTQ2015-71896-REDT, Severo Ochoa program/SEV-2012-0267 and SVP-2013-068057 for A. B. F.-R. grant) and Generalitat Valenciana (Prometeo II/2013/005) are gratefully acknowledged. ; Fraga-Timiraos, AB.; Rodríguez Muñiz, GM.; Peiro-Penalba, V.; Miranda Alonso, MÁ.; Lhiaubet, VL. (2016). Stereoselective Fluorescence Quenching in the Electron Transfer Photooxidation of Nucleobase-Related Azetidines by Cyanoaromatics. Molecules. 21(12). https://doi.org/10.3390/molecules21121683 ; S ; 21 ; 12 ; Arnold, A. R., Grodick, M. A., & Barton, J. K. (2016). DNA Charge Transport: from Chemical Principles to the Cell. Cell Chemical Biology, 23(1), 183-197. doi:10.1016/j.chembiol.2015.11.010 ; Jia, C., Ma, B., Xin, N., & Guo, X. (2015). Carbon Electrode–Molecule Junctions: A Reliable Platform for Molecular Electronics. Accounts of Chemical Research, 48(9), 2565-2575. doi:10.1021/acs.accounts.5b00133 ; Beratan, D. N., Liu, C., ...
The paper presents a study of the processes of mutual diffusion in the binary system Fe - Ni (obtained by the electrocondensation of nickel and iron powders) by the method of X-ray energy dispersive spectroscopy, as well as the processes of thermal and electrical conductivity in the temperature range of 5-300 K. Well-separated regions of almost pure iron and nickel were revealed . The nickel content, estimated by the concentration dependence of the mutual diffusion coefficient, which determines the kinetics of the process of homogenization of the electroconsolidated sample of the Fe - Ni composite, was ~ 70 at. %. The value of the mutual diffusion coefficient of the electroconsolidated Fe - Ni composite is significantly higher than that of an alloy of a similar composition, which is probably the result of the influence of SPS technology (pressure and current in one direction during consolidation), as well as a significant contribution of grain boundary diffusion mass transfer in the composite. It was established that the electrical and thermal conductivity of the electroconsolidated sample is significantly higher than that of samples of the same composition obtained by melting. It was found that the temperature dependence of the electrical resistance of the electroconsolidated sample in the studied interval of 5-300 K is due to the scattering of electrons on defects and on phonons, and the scattering of electrons on phonons can be approximated with high accuracy by the Bloch-Gruneisen-Wilson ratio. The paper shows that the experimental data on the temperature dependence of the effective electrical resistance and thermal conductivity in the range 4.2-300 K of the electroconsolidated Fe0.50Ni0.50 composite are within the Hashin-Shtrikman limits for the conductivities of a three-phase system. The components of the system are pure Fe and Ni, and the intergranular medium in the form of an alloy with an average composition close to Fe0.50Ni0.50 is considered as the third phase.
Six strongly fluorescent four-coordinate organoboron N,C chelates containing an aryl isoquinoline skeleton were prepared. Remarkably, the fluorescence quantum yields reach values of up to 0.74 in oxygen-free toluene. The strong B-N interaction was corroborated by the single-crystal X-ray analysis of two dyes. The intramolecular charge-transfer character of the fluorophores was evidenced by solvatochromism studies and time-dependent DFT calculations at the PCM(toluene)/CAM-B3LYP/6-311++G(2d,p)//PCM(toluene)/B3LYP/6-311G(2d,p) level of theory. The compounds combine high chemical stability with high photostability, especially when equipped with electron-donating substituents. The strong fluorescence and the large Stokes shifts predestine these compounds for use in confocal fluorescence microscopy. This was demonstrated for the imaging of the N13 mouse microglial cell line. Moreover, significant two-photon absorption cross sections (up to 61 GM) allow the use of excitation wavelengths in the near-infrared region (>800 nm) ; The financial support by the Spanish MINECO (CTQ2014-54729-C2-1-P for U.P., CTQ2013-48164-C2-1-P, CTQ2013-48164-C2-2-P for A.R., CTQ2013-41339-P for E.P.I., FPU fellowship for R.L-R., Ramon y Cajal contract RYC-2013-12585 for A.R.), the European Union (FEDER), and the Junta de Andalucia (2012/FQM-2140 for U.P., 2009/FQM-4537, 2012/FQM-1078 for A.R., postdoctoral contract for V.F.P.) is acknowledged. We are grateful for the access to the Supercomputing and Bioinformatics Center (University of Malaga) and the provided technical support. Tristan Neumann (exchange student from the University of Kiel, Germany) performed preliminary experiments.
The excited-state behavior of four-coordinate N,C-chelate organoboron dyes, based on arylisoquinoline ligands with varying degree of charge-transfer character, was characterized. Data related to excited triplet state formation, oxygen quenching, and singlet-oxygen formation were obtained. The results jointly rationalize the previously observed high photostability of the dyes in air-equilibrated media. Furthermore, femtosecond transient absorption experiments enabled the spectroscopic visualization of the excited intramolecular charge transfer (ICT) state that gives rise to the fluorescence of the dyes. ; The funding by the Spanish Ministry of Economy, Industry, and Competitiveness (grants CTQ2014-54729-C2-1-P for U.P., CTQ2014-54729-C2-2-P for F.B., CTQ2013-48164-C2-1-P, CTQ2013-48164-C2-2-P for A.R., Ramon y Cajal contract RYC-2013-12585 for A.R.), the European Union (ERDF), the Andalusian Government (grants 2012/FQM-2140 for U.P., 2009/FQM-4537 and 2012/FQM-1078 for A.R.), and the University of Huelva (postdoctoral contract for V.F.P.) is gratefully acknowledged.
Carbon-bridged bis(aminoaryl) oligo(para-phenylenevinylene)s have been prepared and their optical, electrochemical, and structural properties analyzed. Their radical cations are class III and class II mixed-valence systems, depending on the molecular size, and they show electronic couplings which are among the largest for the self-exchange reaction of purely organic molecules. In their dication states, the antiferromagnetic coupling is progressively tuned with size from quinoidal closed-shell to open-shell biradicals. The data prove that the electronic coupling in the radical cations and the singlet–triplet gap in the dications show similar small attenuation factors, thus allowing charge/spin transfer over rather large distances. · ; We thank MINECO of the Spanish Government (CTQ2015- 69391-P, CTQ2013-40480-R and MAT2015-66856-R) for their support. We also thank the Research Central Services (SCAI) of the University of M#laga. This work is partially supported by Grant-in-Aid for Scientific Research (16H04106 to HTand 15H05754 to EN) and the Strategic Promotion of Innovative Research, JST (to EN) from MEXT, Japan. M.H. and C.L. are grateful to the Deutsche Forschungsgemeinschaft for supporting this work (GRK 2112). ; Peer reviewed
State-of-the-art organic solar cells (OSCs) typically suffer from large voltage loss (V-loss) compared to their inorganic and perovskite counterparts. There are some successful attempts to reduce the V-loss by decreasing the energy offsets between the donor and acceptor materials, and the OSC community has demonstrated efficient systems with either small highest occupied molecular orbital (HOMO) offset or negligible lowest unoccupied molecular orbital (LUMO) offset between donors and acceptors. However, efficient OSCs based on a donor/acceptor system with both small HOMO and LUMO offsets have not been demonstrated simultaneously. In this work, an efficient nonfullerene OSC is reported based on a donor polymer named PffBT2T-TT and a small-molecular acceptor (O-IDTBR), which have identical bandgaps and close energy levels. The Fourier-transform photocurrent spectroscopy external quantum efficiency (FTPS-EQE) spectrum of the blend overlaps with those of neat PffBT2T-TT and O-IDTBR, indicating the small driving forces for both hole and electron transfer. Meanwhile, the OSCs exhibit a high electroluminescence quantum efficiency (EQE(EL)) of approximate to 1 x 10(-4), which leads to a significantly minimized nonradiative V-loss of 0.24 V. Despite the small driving forces and a low V-loss, a maximum EQE of 67% and a high power conversion efficiency of 10.4% can still be achieved. ; Funding Agencies|National Basic Research Program of China (973 Program) [2013CB834701, 2014CB643501]; Shenzhen Technology and Innovation Commission [JCYJ20170413173814007, JCYJ20170818113905024]; Hong Kong Research Grants Council [T23-407/13 N, N_HKUST623/13, 16305915, 16322416, 606012, 16306117, 16303917]; HK JEBN Limited, HKUST presidents office [FP201]; National Science Foundation of China [21374090]; Swedish Energy Agency Energimyndigheten [2016-010174]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009-00971]; Hong Kong Innovation and Technology Commission [ITC-CNERC14SC01, ITS/083/15]
In the present paper U.V. spectroscopic evidence is given for the formation of charge transfer complexes between three substituted α, α'-dicyanostilbenes (4, 4' dichloro-, 4, 4' dicyano-4, 4' dinitro-) used as acceptors and saturated amines used as donors. It was also found that the electronic spectra of the different systems studied showed unexpected time dependent behaviour. This behaviour is brought about by the trans-cis isomerisation of the acceptors, induced by the donor molecules. A qualitative study of the stereo-isomerisation is given as a proof.
α-Methyldithiophene–tetrathiafulvalene (α-mDT-TTF), the first alkyl-substituted thiophene–tetrathiafulvalene electronic donor, and some of its charge-transfer salts were explored. The crystal structure of α-mDT-TTF is composed of molecular stacks aligned parallel to each other. Its cyclic voltammetry shows higher electron-donor ability than the unsubstituted analogue. This material was employed as a semiconductor in an organic field-effect transistor and showed a mobility of 4 10–4 cm2V–1 s–1. Two charge-transfer salts of this donor with [M(mnt)2]– anions (mnt = maleonitriledithiolate), M = Co and Au, were obtained by electrocrystallization; they present unusual stoichiometries: (α-mDTTTF)[ Co(mnt)2] and (α-mDT-TTF)3[Au(mnt)2]2. In the cobalt compound, the donor molecules are fully oxidized and the Co complex is dimerized; it presents semiconducting behavior (7 10–3 Scm–1). The gold compound is composed of alternating stacks of donor trimers and pairs of anions. ; This work was supported by Portuguese Fundação do Ministério de Ciência e Tecnologia (FCT) through contract PTDC/QEQ-SUP/ 1413/2012, UID/Multi/04349/2013, RECI/QEQ-QIN/0189/2012 and PhD grant SFRH/BD/86131/2012.We also acknowledge financial support of the European Union (EU) project ERC StG 2012- 306826 e-GAMES and the Networking Research Center of Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the Spanish Ministerio de Ciencia e Innovación (MICINN), and Fondos Europeos para el Desarrollo Regional (FEDER) with project BE-WELL CTQ2013-40480-R and the Generalitat de Catalunya with project 2014-SGR. We acknowledge the European Synchrotron Radiation Facility for provision of synchrotron radiation facilities, and we would like to thank Jonathan Wright for assistance in using beamline ID11. [ ; Peer reviewed
In this paper we studied the performance of bioanodes under different experimental conditions using polarization curves and impedance spectroscopy. We have identified that the large capacitances of up to 1 mF·cm− 2 for graphite anodes have their origin in the nature of the carbonaceous electrode, rather than the microbial culture. In some cases, the separate contributions of charge transfer and diffusion resistance were clearly visible, while in other cases their contribution was masked by the high capacitance of 1 mF·cm− 2. The impedance data were analyzed using the basic Randles model to analyze ohmic, charge transfer and diffusion resistances. Increasing buffer concentration from 0 to 50 mM and increasing pH from 6 to 8 resulted in decreased charge transfer and diffusion resistances; lowest values being 144 Ω·cm2 and 34 Ω·cm2, respectively. At acetate concentrations below 1 mM, current generation was limited by acetate. We show a linear relationship between inverse charge transfer resistance at potentials close to open circuit and saturation (maximum) current, associated to the Butler–Volmer relationship that needs further exploration. ; The authors wish to acknowledge funding from the European Union Seventh Framework Programme (FP7/2012-2016) project 'Bioelectrochemical systems for metal production, recycling, and remediation' under grant agreement no. 282970. AtH is supported by a NWO VENI grant no. 13631. OS was supported by the French environmental agency ADEME, by the Region Bretagne and by Rennes Metropole when doing the experiments. This work was performed in the cooperation framework of Wetsus, Centre of Excellence for Sustainable Water Technology (www.wetsus.nl). Wetsus is co-funded by the Dutch Ministry of Economic Affairs and Ministry of Infrastructure and Environment, the European Union Regional Development Fund, the Province of Fryslân, and the Northern Netherlands Provinces.
